diff --git a/omniauth-cas.gemspec b/omniauth-cas.gemspec
index 45e7b60..6a67998 100644
--- a/omniauth-cas.gemspec
+++ b/omniauth-cas.gemspec
@@ -28,5 +28,5 @@ Gem::Specification.new do |gem|
 
   gem.add_dependency 'addressable', '~> 2.8'
   gem.add_dependency 'nokogiri',    '~> 1.12'
-  gem.add_dependency 'omniauth',    '~> 1.9'
+  gem.add_dependency 'omniauth',    '>= 1.9', '< 3.0'
 end